Searching with Google is not an exciting issue, nonetheless it could give away some interesting things as you know. Profiling users through google is pretty easy. There is a free stat script called BBCLONE, i use it myself, and thought about google it. then you can see which sites are using it, and you can see their stats. So far so good, the interesting part comes with the build in feature that it shows your referer, so if they search through google it shows the search query that was made before entering the site.

check this as an example:

http://djdarkman.extra.hu/bbclone/show_detailed.php?lng=en

and try to hover above the google referer links, you can see the searchquery. This way u can profile Torrent searchers, Porn surfers, etc.

The most striking issue i came accros, is that in my country (NL) there are providers who give an internetaccount to customers, with their "lastname" as subdomain on which they surf, like: "lastname.internetprovider.nl"

So with that hostname which BBCLONE also logs, we could Google on that, and see where that person went next, or posted on forums, and maybe have a myspace, or some community site where we could find out their email, name, phone, and even address, and thereby being profiled.

Imagine someone could build a bot that follows all those trails and logs everything into a vector, profile by profile...

This seems too easy.

Paranoid? maybe, but what could the implications be?
maybe not now, but in the near future?

A method against it is the FireFox "noreferer" type extension, this removes the referer on the Url, when right-clicked.

Yup, worse yet, they can tell what links you've clicked on when you enter, by fetching the same URL you went to and using Jeremiah's CSS hack I can actually tell what other links you've clicked on from the search engine.